1. Colour and seam strip
Due to high temperature heating and deburring treatment, the welding seam of high-frequency welding pipe and its heat affected area are cyan, and its color is obviously darker than that of the surrounding area, showing a strip distribution with basically the same width and no obvious depth change. Seamless steel generally does not have such a long continuous strip traces, sometimes rolling allows defects will appear similar to the strip is very urgent, but it is difficult to continue to distribute.
2. Welding joints
Generally speaking, there are two kinds of welding joints such as straight seam and spiral welding joints. For steel pipe without surface coating, if the weld joint can be clearly seen, it must be welded pipe. There are two common types of direct welding resistance welding and submerged arc welding, general resistance welding (RW, ERW or HFW) welding seam burr requirements are different.
But for the high-frequency welding pipe that need better requirements of straight seam, it require to remove the internal and external burrs after welding, generally there will be obvious convex, but or more or less there will be some banding convex (burr removal is insufficient) or groove (burr removal is too much). Some scaffolding welded pipe is usually supplied with burrs supply due to low requirements and small size. Large size high-frequency welded pipe with burr as shown in the figure below, it is undoubtedly a welded pipe.
If the ERW pipe is deburred and treated with internal and external corrosion protection, it is difficult to see whether there is a weld seam on the surface. Straight seam submerged arc welding (UOE, JCOE, etc.) involves the addition of wire to the welding process so that there is a significant bump at the weld and the weld can be found even after coating.
SRW pipes, often used in large size welded pipe, show a spiral curve along the longitudinal of the pipe, like wound around the surface of the pipe. There will be some noticeable bulges at the welds on the inner and outer surfaces. Welds joints can be seen even after coated. Sometimes spiral welded pipe also be circumferential welding butt welded, there may be several rings of circumferential welds, generally there are convex welds on the inner and outer walls.
3. Wall thickness accuracy and ellipticity
Seamless steel tube is manufactured by plate rolling with direct perforation of tube billet, which is a three-dimensional complex deformation and difficult to control the precision of wall thickness. Generally, the wall thickness tolerance level of steel tubes is about 12.5%, and the higher level can reach ±8% -10%, or even± 5%, most of these steel tubes are thick wall tubes.
The welded pipe is directly from the hot rolled/thick plate made of steel plate or steel coil welding, its wall thickness quality depends on the thickness of the steel plate control accuracy, generally can reach within 0.10mm plus or minus. Therefore, the pipe with high wall thickness accuracy is generally more likely to be welded. At the same time, ERW welded tubes and UOE tubes generally have good roundness due to the manufacturing process and diameter enlargement, the level of ovality can also be used as a basis for judging whether or not to weld the pipe. the pipe with small ellipticity is possible the welding pipe.
Post time: Apr-05-2021